WO2014161833A1

WO2014161833A1 - Welded structural link between a high-performance thermoplastic matrix composite material and an elastomer

Info

Publication number: WO2014161833A1
Application number: PCT/EP2014/056493
Authority: WO
Inventors: Audrey MENOCHET
Original assignee: Astrium Sas
Priority date: 2013-04-03
Filing date: 2014-04-01
Publication date: 2014-10-09
Also published as: EP2981571B1; EP2981571A1; US10131093B2; JP2016514638A; US20160059478A1; FR3004186A1; FR3004186B1

Abstract

The invention concerns a method for producing, by welding, a link between a thermoplastic matrix composite material (36) and an elastomeric material (33). The method mainly comprises an operation of functionalising the elastomeric material (33) by incorporating, onto the surface of said elastomer, a nonwoven fabric (24) consisting of fibres of thermoplastic material and a welding operation consisting of welding the functionalised surface of the elastomeric material (33) to the thermoplastic material of the composite (36). The operation of functionalising the elastomeric material (33) is carried out during the phase of vulcanising the raw elastomer, the vulcanisation being carried out under sufficient pressure for the nonwoven fabric (24) placed on the surface of the raw elastomer (25) to become incorporated with same, at least at the surface, during the vulcanisation process. The welding operation consists of interposing a metal fabric (35) coated with thermoplastic material between the surfaces of the elastomer (33) and the composite (36) that are to be welded to each other, and of passing an electric current through same, resulting in the surface melting of the two materials.

Description

Structural bond welded between a high performance thermoplastic matrix composite material and an elastomer

FIELD OF THE INVENTION

The invention relates to the field of structural chemical assemblies of different materials, and more specifically the assembly of elastomeric materials with thermoplastic materials.

Very generally, the term "thermoplastic material" refers to any material comprising a certain percentage of thermoplastic material constituting a matrix, whether it is a material consisting solely of thermoplastic material or, for example, of a continuous fiber composite material. and thermoplastic matrix.

The invention finds, for example, a particular application in the context of the manufacture of propellant stages of powder rockets, to achieve the connection of the reservoir with the skirts.

BACKGROUND OF THE INVENTION - PRIOR ART

Welding assembly of two high performance thermoplastic matrix composite materials generally employs known assembly methods. Moreover, in order to bring the assembly area to the desired temperature, it is possible to implement several known principles of heating such as heating by hot gas (oven, autoclave), by vibration (ultrasound, rotation), by induction, resistance, etc. This type of assembly is described in particular in the book by Michael J. Troughton entitled "Handbook of plastics joining" (Plastics Design Library). ISBN: 978-1-884207-17-4.

Conversely, there is, to date, no known means for performing the welding assembly of a thermoplastic matrix composite material and an elastomeric type material. This absence seems to stem from the fact that, in so far as the elastomers do not have the property of reversibly passing from the solid state to the molten state, a assembly technique requiring the heating of the materials to be assembled, at least at the level of the assembly area, does not seem obvious to the skilled person. For some applications, the known assembly techniques for assembling a thermoplastic material element with a polymer material element do not have the required qualities, in terms of mechanical strength in particular.

This is the case for example, as shown schematically in FIG. 1, for the assembly of a shell 11 (made of metallic material or composite with a thermoplastic or thermosetting matrix) on a tank 12 made of composite with a thermoplastic matrix to constitute a propellant stage of powder launcher, or a consumer gas tank.

Indeed, this assembly requires the insertion of a layer 13 of elastomeric material within the bond, the layer of elastomeric material having the role of absorbing significant differential deformations that appear between the two structures. As a result of the insertion of this layer 13 of intermediate elastomeric material requires the assembly of this layer on the two composite material elements that constitute the reservoir 12 and the shell 1 1, this assembly must necessarily be of high mechanical quality, because of the constraints imposed on the assembly.

However, in terms of mechanical strength a welded connection is generally greater than a bonded bond. Indeed, after welding, there is no differentiated interface between the two assembled parts, because of the diffusion of the molecules from one part to another, whereas in the case of a bonding, there is as many interfaces as layers necessary for the creation of the bond, layers among which are mainly in addition to the adhesive layer itself, the adhesion primers, as well as the treatments applied to the surfaces to be assembled.

Moreover, in the case of welding, the constraints generated by the preparation of the surfaces before assembly and by their protection against pollution are also eliminated, these operations being necessary, even imperative, in the case of a bonding assembly. PRESENTA TION OF THE INVENTION

An object of the invention is to provide a solution for performing the structural assembly by welding a thermoplastic material and an elastomeric material, the focus being on these two families of materials.

To this end, the subject of the invention is a method for producing a welded structural connection between a thermoplastic matrix composite material and an elastomer, characterized in that it comprises the following operations: a first operation of functionalization of the elastomer material by means of a non-woven fabric formed of fibers of thermoplastic material, the functionalization being carried out by penetration of the textile into the surface layer of the elastomeric material during the pressure vulcanization operation of said elastomeric material;

a second welding operation itself, during which the thermoplastic composite material is welded to the functionalized layer of the elastomeric material. According to various particular provisions, which can be considered in conjunction, the method according to the invention may furthermore have the following characteristics.

According to one particular arrangement, the operation of producing the functionalized elastomer itself comprises several steps:

a first cleaning step of the different parts of the vulcanization mold used;

a second step during which the nonwoven fabric is applied to the surface of the elastomeric material

a third step during which the underpressure vulcanization of the elastomeric material is carried out; the applied pressure being determined so that the nonwoven fabric placed on the surface of the elastomer is incorporated therewith, at least at the surface, during the vulcanization process.

According to another particular provision, the nonwoven fabric is produced by implementing the following operations:

- carding monofilaments of thermoplastic material; - Making veils superimposed on each other and maintained between them by needling;

- reinforcement of the textile by hydrolysis. According to another particular arrangement, the nonwoven fabric is made of a thermoplastic material chosen so that it can both be welded to the thermoplastic material forming the matrix of the composite material and have good compatibility with the elastomeric material.

According to a variant of this particular arrangement, the nonwoven fabric is made of a thermoplastic material identical to that forming the matrix of the composite material. According to another particular arrangement, the composite material being a carbon / polyetheretherketone composite and the elastomeric material being of the HNBR type, the nonwoven fabric used is formed of polyetherimide fibers. According to another particular arrangement, the second welding operation consists in heating the contact surfaces of the two materials to be welded by interposing between these two surfaces a wire cloth which acts as a heating resistor, the wire mesh being itself impregnated with thermoplastic material. .

According to another particular arrangement, the welding operation is preceded by a preliminary operation for preparing the surfaces of the materials to be assembled, which operation may consist, depending on the state of these surfaces, either in a simple degreasing with the aid of a suitable solvent, either by fine sanding the functionalized surface of the elastomeric element, followed by cleaning the surfaces with the same solvent.

According to another particular arrangement, the composite material being a carbon / polyetheretherketone composite and the elastomeric material being of the HNBR type, the operation of functionalization of the elastomeric material comprises the following operations: a) a first operation of placing, on the bottom plate of the vulcanization mold, the following elements:

two superimposed layers of teflon glass fabric;

a ply of nonwoven fabric made of polyetherimide fibers;

the folds of the unvulcanized raw elastomeric material;

- a set of border wedges;

two superimposed layers of teflon glass fabric;

the assembly being capped by the upper plate of the vulcanization mold;

b) a second operation of placing the stack formed on the plate of a heating press preheated to a temperature θ ₂ of 140 ° C;

c) a third hot pressing operation of the stack, during which the nominal pressing cycle adapted to the elastomer considered is applied.

d) a fourth operation during which the mold is removed from the press while the latter maintains the temperature θ ₂ of 140 ° C, the functionalized elastomer is demolded and allowed to cool to room temperature.

According to a variant of this particular arrangement, the pressing cycle of the third operation comprises:

a phase of gradual rise in temperature up to a high temperature θι of 230 ° C. with a gradient of 2.5 ° C./min,

a phase of maintaining the temperature θι for 10 minutes,

a phase of descent in temperature up to the temperature θ ₂ of 140 ° C. according to a gradient in 2.5 ° C./min;

According to another particular arrangement, the composite material being a carbon / polyetheretherketone composite and the elastomeric material being of the HNBR type, the actual welding operation comprises the following steps:

a) A first implementation step during which the following elements are mainly arranged, in order, on a plate of thermal insulating material:

a first heat-resistant polyimide film,

the functionalized elastomeric material,

a first polyetherimide film, a metal cloth pre-impregnated with polyetherimide,

a second polyetherimide film,

the thermoplastic composite material,

a second polyimide film,

a layer of thermal insulation,

- a glass cloth;

b) A second step during which a vacuum bladder is made with a polyimide film arranged so as to let the wire cloth out, the sealing of said bladder being ensured by means of high temperature mastic.

c) A third step during which the bladder is evacuated, a power supply unit is connected to the wire mesh and different intensity values are applied in a suitable cycle.

d) A fourth step during which the polyimide film used as a vacuum cover is removed and the stack is removed.

According to another particular arrangement, during the third step is applied to the wire mesh a current of 15.6 amps for 200 seconds and a current of 10 amperes for 100 seconds.

DESCRIPTION OF THE FIGURES

The characteristics and advantages of the invention will be better appreciated thanks to the following description, which is based on the appended figures which show:

- the figurel, a schematic illustration of an example of a structure for which the assembly by welding of the various elements seems particularly suitable, because of the mechanical stresses imposed on this assembly;

FIG. 2, an illustration of an exemplary implementation of the functionalization step of the elastomer of the process according to the invention;

- Figure 3, an illustration of an example of implementation of the welding operation according to the invention.

DETAILED DESCRIPTION The principle of the method according to the invention consists mainly in the implementation before the actual welding, an operation of preparation of the elastomeric material. This operation consists of functionalizing, that is to say modifying, the surface or the core of the elastomer to give it the necessary properties to be welded to the thermoplastic material. By "functionalizing the elastomeric material" is therefore meant to "modify" the composition of the surface layers of this elastomeric material by incorporating a thermoplastic material therein.

For this purpose, a nonwoven fabric made of fibers of a thermoplastic material having both a compatibility with the elastomeric material and being welded to the matrix of the material is inserted into the elastomeric material, or at least on its surface. thermoplastic composite to which we want to assemble the elastomeric material considered.

Compatibility between the elastomeric material and the thermoplastic material forming the nonwoven fabric is mainly meant, in this case, physico-chemical compatibility between the two materials. This compatibility results in a possible interaction between the thermoplastic material of the nonwoven fabric and the elastomer, an interaction that a person skilled in the field of plastics chemistry knows to characterize by specific criteria, of a rather chemical nature: wettability, interdiffusion between materials, chemical bonding.

However, there is also interest in compatibility of implementation between the different materials (physical compatibility), in particular as regards the need to be able to vulcanize the elastomer temperature without deteriorating the thermoplastic material forming the incorporated textile.

The operation of elaboration of the functionalized elastomer comprises several steps:

a first cleaning step of the various parts of the vulcanization mold, cleaning carried out, for example, with methyl ethyl ketone (or MEC).

a second step during which the nonwoven fabric is applied to the surface of the raw elastomeric material (ie not yet vulcanized) and the elastomeric material is subjected to vulcanization under pressure. According to the invention, the pressure applied is determined so that the textile nonwoven placed on the surface of the elastomer is incorporated therewith, at least at the surface, during the vulcanization process.

Thus, for example, in a particular embodiment of the invention, adapted more particularly to the welding of a polyetheretherketone (PEEK) matrix composite material and to a carbon fiber reinforcement (carbon / PEEK thermoplastic composite) with a elastomer of the hydrogenated nitrile rubber (hydrogenated butadiene-acrylonitrile) type, or Buna or HNBR (acronym for the English name ", hydrogenated nitrile butadiene rubber", the actual elaboration of the functionalized elastomer may itself comprise the operations following:

a) A first operation of setting up, on the lower plate 21 of the vulcanization mold, the elements necessary for the implementation of the functionalization of the elastomeric material, namely, in the order and as illustrated in FIG. 2:

two superimposed layers 22 and 23 of teflon glass fabric, the function of which is to allow the demolding of the elastomer after polymerization;

a ply of nonwoven textile 24, made of Polyetherimide (or PEI) fibers,

the folds of the raw elastomeric material 25 (unvulcanized), to be functionalized,

a set of wedges 26, 27, wedges made of stainless steel type 304L for example,

two superimposed layers 28 and 29 of teflon glass fabric, ensuring a role similar to that provided by the layers 22 and 23.

After placement, the assembly is capped by the upper plate 21 1 of the vulcanization mold so that all the elements listed above are placed between the lower plate 21 and the upper plate 21 1 of the mold;

b) a second operation of placing the stack formed on the plate of a heating press preheated to a temperature θ _{2 of} 140 ° C; c) a third heat-pressing operation of the stack, during which the nominal pressing cycle adapted to the considered elastomer is applied, this cycle comprising:

a phase of gradual rise in temperature to a high temperature θ ₁ (230 ° C. at 2.5 ° C./min),

a maintenance phase at the temperature θι (10-minute stage at 230 ° C.),

a phase of descent in temperature up to the temperature θ ₂ (140 ° C. at 2.5 ° C./min);

d) a fourth operation during which the mold is removed from the press while the latter maintains the temperature θ ₂ (140 ° C), the functionalized elastomer is demolded and allowed to cool to room temperature.

A surface-functionalized vulcanized elastomer is thus obtained, comprising a conventional elastomer base having a surface layer of elastomer functionalized by the layer of nonwoven fabric 24 formed of fibers made of thermoplastic material, a layer of 0.4 mm thick. thickness for example. It should be noted that according to the invention, the nonwoven fabric used is preferably constituted by short fibers of thermoplastic material, PEI for example, entangled and distributed in a random orientation. The method of manufacturing this nonwoven fabric mainly comprises the following operations:

- carding monofilaments of thermoplastic material;

- Making veils superimposed on each other and maintained between them by needling;

- reinforcement of the textile by hydrolysis. In a particular embodiment, the nonwoven fabric is chosen from the same material as that which constitutes the matrix of the composite material to which the elastomer material must be welded, a textile of density 100 g / m ² , needled and hydrolyzed under a pressure of 40 bars for example.

It should be noted, however, that this nonwoven fabric may be made of a different material, in particular to satisfy at best the double requirement good adhesion of the two thermoplastic materials (ie that of the composite material and that of the functionalization textile of the elastomer) and good compatibility of the material constituting the functionalization textile and the elastomeric material.

Once the polymer material has been functionalized, the process according to the invention continues with the actual welding step, an operation which, thanks to the functionalization of the polymer material, advantageously proceeds in a manner analogous to a welding operation of two pieces of material thermoplastic matrix composite. This operation can in particular be carried out by induction or by resistance.

It should be noted that advantageously, the welding operation is not subjected to any delay constraint to be achieved, unlike what is likely to occur for a bonding assembly. Insofar as the functionalized elastomeric material is vulcanized before assembly, the welding of the two materials can thus be carried out at the moment considered to be the most appropriate, a time that may be more or less distant in time from that of completion of the functionalization.

The resistance method consists in locally heating the interface between the composite material and the functionalized elastomer, to obtain a bond between the thermoplastic matrix of the composite material and the thermoplastic portion of the functionalized elastomer. According to the invention, the actual welding step begins with a preliminary operation of preparing the surfaces to be assembled. Depending on the state of these surfaces the preparation may consist of a simple degreasing with the aid of a suitable solvent, ethanol for example, or by fine sanding of the functionalized surface of the elastomer element, with a Sic 400 grit sandpaper, for example, followed by cleaning, using the same solvent, the surfaces and in particular the sanded surface. By appropriate solvent is meant here a solvent of the fatty substances which by its nature or composition does not present any risk of causing a dissolution of the material itself.

It then continues by an operation of heating the contact surfaces of the two materials to be welded by interposing between these two surfaces a wire mesh which acts as a heating resistor; the operation being carried out under vacuum. According to the invention, the wire cloth is itself impregnated with thermoplastic material.

For example, in a particular embodiment of the invention, adapted more particularly to the welding of a PEEK matrix composite material and a carbon fiber reinforcement (carbon / PEEK thermoplastic composite) with an elastomer of the HNBR type. (Buna), the actual welding operation itself may comprise the following steps: a) A first implementation step during which, as illustrated by FIG. 3, there is mainly, in order, on a plate 31 of thermal insulating material, of NL FIH for example, the following elements:

a first heat-resistant polyimide film 32, preferably an Upilex® film, intended to promote the disassembly of the assembly after welding,

the functionalized elastomer material 33,

a first film 34 of polyetherimide (PEI), of the Ultem 1000 type for example,

a wire cloth pre-impregnated with PEI, for example a reference fabric 102083 manufactured by the Gantois firm,

a second film 36 of polyetherimide (PEI),

the thermoplastic composite material 36 (C / PEEK) coated with PEI,

a second film 37 of Upilex polyimide also intended to promote the disassembly of the assembly after welding,

a layer of thermal insulation 38 (NL FIH),

a glass fabric 31 1, of the E5555 type for example, designed to promote the drainage of the air present. b) A second step during which a vacuum bladder is made with a film 312 of polyimide (Thermalimide) arranged so as to leave the PEI-impregnated wire cloth out; the seal being obtained with a high temperature sealant A800 3G. c) A third step during which the bladder 312 thus made is evacuated, a power supply unit is connected to the wire mesh 35 and different intensity values are applied according to a suitable cycle: for example 15.6 amperes for 200 seconds then 10 amps for 100 seconds. d) A fourth step during which the polyimide film 312 used as a vacuum tarpaulin is removed and the stack is removed so as to recover the thermoplastic elastomer-composite assembly thus produced.

Claims

1. Method for producing a welded structural connection between a composite material with a thermoplastic matrix and an elastomer, characterized in that it comprises the following operations:

- a first operation of functionalization of the elastomeric material by means of a non-woven textile formed of fibers of thermoplastic material, the functionalization being carried out by penetration of the textile into the surface layer of the elastomeric material during the operation of vulcanization under pressure of said elastomeric material ;

- a second welding operation itself, during which the thermoplastic composite material is welded to the functionalized layer of the elastomeric material.

2. Method according to claim 1, characterized in that the operation of producing the functionalized elastomer itself comprises several stages:

- a first step of cleaning the different parts of the vulcanization mold used;

- a second step during which the non-woven textile is applied to the surface of the elastomeric material

- a third step during which the elastomer material is vulcanized under pressure; the pressure applied being determined so that the non-woven textile placed on the surface of the elastomer is incorporated into it, at least on the surface, during the vulcanization process.

3. Method according to one of claims 1 or 2, characterized in that the non-woven textile is produced by implementing the following operations:

- carding of monofilaments of thermoplastic material;

- production of sails superimposed on each other and held together by needling;

- reinforcement of the textile by hydrobonding.

4. Method according to any one of claims 1 to 3, characterized in that the non-woven textile is made of a thermoplastic material chosen so as to be able to both be welded to the thermoplastic material forming the matrix of the composite material and to present good compatibility with the elastomeric material.

5. Method according to claim 4, characterized in that the non-woven textile is made of a thermoplastic material identical to that forming the matrix of the composite material.

6. Method according to any one of claims 1 to 5, characterized in that, the composite material being a carbon/polyetheretherketone composite and the elastomer material being of the HNBR type, the non-woven textile used is formed of polyetherimide fibers.

7. Method according to any one of the preceding claims, characterized in that the second welding operation consists of heating the contact surfaces of the two materials to be welded by interposing between these two surfaces a metal canvas which acts as a heating resistance, the metal mesh being itself impregnated with thermoplastic material.

8. Method according to claim 7, characterized in that the welding operation is preceded by a preliminary operation of preparing the surfaces of the materials to be assembled, this operation being able to consist, depending on the state of these surfaces, either of a simple degreasing using an appropriate solvent, or by fine sanding of the functionalized surface of the elastomer element, followed by cleaning the surfaces with the same solvent.

9. Method according to any one of the preceding claims, characterized in that, the composite material being a carbon/polyetheretherketone composite and the elastomer material being of the type HNBR, the operation of functionalization of the elastomeric material comprises the following operations: a) a first operation of placing, on the lower plate (21) of the vulcanization mold, the following elements:

- two superimposed layers (22, 23) of Teflon glass fabric;

- a ply of non-woven textile (24) made of polyetherimide fibers;

- the folds of the unvulcanized raw elastomeric material (25);

- a set of edging wedges (26, 27);

- two superimposed layers (28, 29) of Teflon glass fabric;

the assembly being capped by the upper plate (21 1) of the vulcanization mold;

b) a second operation of placing the stack made on the plate of a heating press preheated to a temperature θ ₂ of 140°C;

d) a fourth operation during which the mold is removed from the press while the latter maintains the temperature θ ₂ of 140° C., the functionalized elastomer is unmolded and it is allowed to cool to room temperature.

10. Method according to claim 9, characterized in that the pressing cycle of the third operation comprises:

- a phase of gradual rise in temperature up to a high temperature θι of 230 ° C with a gradient of 2.5 ° C/min,

- a phase of maintaining the temperature θι for 10 minutes,

- a temperature drop phase to the temperature θ ₂ of 140°C according to a gradient of 2.5°C/min;

1 1 . Method according to any one of the preceding claims, characterized in that, the composite material being a composite carbon/polyetheretherketone and the elastomeric material being of the HNBR type, the welding operation itself comprises the following steps:

a) A first installation step during which the following elements are mainly placed, in order, on a plate (31) of thermal insulating material:

- a first film (32) made of heat-resistant polyimide,

- the functionalized elastomer material (33),

- a first film (34) of polyetherimide,

- a metal mesh (35) pre-impregnated with polyetherimide,

- a second film (36) of polyetherimide,

- the thermoplastic composite material (36),

- a second polyimide film (37),

- a layer of thermal insulation (38),

- a glass fabric (31 1);

b) A second step during which a vacuum bladder is produced with a polyimide film (312) arranged so as to let the metal mesh (35) emerge, the sealing of said bladder being ensured by means of mastic at high temperature.

c) A third step during which the bladder (312) is placed under vacuum, an electrical power supply unit is connected to the metal mesh (35) and different intensity values are applied following an appropriate cycle.

d) A fourth step during which the polyimide film (312) serving as a vacuum cover is removed and the stack is dismantled.

12. Method according to claim 1 1, characterized in that during the third step a current of 15.6 amps is applied to the metal mesh (35) for 200 seconds then a current of 10 amps for 100 seconds.